An Introduction to a Biology 



distinct classes, according as we are dealing collectively with 

 a vast number of things — with a mass phenomenon ; or with 

 the individual units which make up that mass. These two 

 kinds of knowledge are radically different, and are distin- 

 guished from one another by the same characters as those 

 which are peculiar to the two meanings of the statement 

 that a thing happens by chance ; for when we make tliis 

 statement we may either be referring to the method by 

 which I decided whether to write " biometric " or " Men- 

 delian " first in the title of this paper, or to the result of 

 a very great number of tosses — an approximation to 50% 

 heads and 50% tails, which is close in proportion as the 

 number of trials is great. The first difference that I mention 

 between these two meanings of chance, as illustrative of 

 the characters of the two classes into which we have divided 

 our aspect of things, is that, while in the case of the first 

 it is impossible to predict the result of a single trial, there 

 is nothing easier to foretell than the result of a very large 

 number ; nothing is more uncertain than the former, nothing 

 more certain than the latter. A second difference between 

 these two groups is that that which is true of the mass is 

 not necessarily true of all the component individuals, though 

 it may be of some ; in the case of coin-tossing, the statement 

 that the result of an infinitely large number of trials is an 

 equal number of heads and tails is contradicted at every 

 single toss, though this would not be the case if some of 

 the coins we tossed had half the head and half the tail on 

 each side of the coin.^ Is it necessary to add that from the 

 fact that what is true of the mass is not true of the individual 

 it does not follow that acsertions about the individual are 

 antagonistic to statements about the mass ? It is important 

 to reahse this truth because it is seldom done and appar- 



^ I have found Galton's apparatus for illustrating the origin of the curve 

 of frequency (" Natural Inheritance," p. 03, Fig. 7) very useful for explain- 

 ing the difference between these two classes. An example of the first is 

 afforded by allowing a single shot to run down the inclined board ; an 

 example of the second by displaying the result of a thousand such events. 



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